diff --git a/src/core.c b/src/core.c
index 07bc828..87ef420 100644
--- a/src/core.c
+++ b/src/core.c
@@ -359,7 +359,10 @@
 
 int mtdev_open(struct mtdev *dev, int fd)
 {
-	int ret;
+	int ret = -EINVAL;
+
+	if (!dev || fd < 0)
+		goto error;
 	ret = mtdev_init(dev);
 	if (ret)
 		goto error;